pcamis,
You are right, that junos version is EoL and the SRX model as well, so I dont expect Engineering to work on this, or at least we could not demand it. As confirmed you can move to the previous version where the problem is not showing.
Regarding the syslog file commands I shared previously, it wasnt for logging purposes. I saw one case (in a high end SRX) where they were facing the same problem and the workaround was to upgrade to the faulty version again, then configure the messages log file in the way I specified and commit the configuration. After this they were able to access via J-Web. I know it doesnt make sense but thats what a bug is all about. Maybe you can try luck with these steps.
I hope this gets resolved.